In the past, exterior walls of buildings were commonly constructed of solid masonry, involving multiple wythes (or thicknesses) of masonry laid up together. Floor joists were supported in recesses in the inner masonry wythe and floors, room partition walls, and the rest of the inside of the building were supported on these joists. In some cases, insulation was installed between wythes.
In the past few decades, solid masonry wall construction has been replaced by masonry veneer wall construction. For example, in single family residential construction, a frame of a house is constructed, usually of wooden studs, sheathing material is affixed to the outer surface of the studs and a single masonry wythe (often brick) is erected as a veneer outside of the sheathing material. In residential construction, insulating material is most often installed in the space between adjacent wooden studs. The masonry veneer wall is attached to the back-up wall of wooden studs using an array of anchors. The outer end of each anchor terminates as an embedment within the mortar bed between the courses of masonry, placed as the wall is erected. The inner end of each anchor is usually fastened to a wooden stud in the wooden back-up wall framing.
More recently, especially in commercial buildings, the back-up wall to which the masonry veneer is attached has been made of steel studs and some, or all, of the insulating material is installed outboard of the steel stud framing. In this form of masonry veneer construction, the attachment between the metal studs and the masonry also involves an array of anchors. These anchors are commonly one-piece formed metal, with a slot or set of holes near the outer end of the anchor. In one common form of attachment, the anchor resembles a bayonet that is fastened to the side of the steel stud and pierces the exterior sheathing (and any other materials outboard of the sheathing). In such a case, the inner portion of each anchor can be screwed or bolted to a steel stud. A bent tie wire is inserted through slots or holes in the outer end of the anchor and then embedded in the mortar bed between courses of masonry.
Current building codes require an air, moisture and vapor barrier membrane to be installed within most exterior wall assemblies. In commercial and some residential construction, designers often use a single membrane applied over the exterior surface of sheathing to meet this requirement in veneer wall construction with steel stud back-up walls. However, for walls using bayonet style masonry anchors, common in the industry today, the membrane must be interrupted by the bayonets that protrude from the sheathing, thereby piercing the membrane. For the membrane to remain as a functional air, moisture and vapor barrier, mastic/caulking must be applied around each spot where a bayonet pierces the membrane. The mastic/caulking is applied manually and its application is a time consuming process if a proper seal around each bayonet is to be achieved. In reality, it is unlikely that the membrane will be completely sealed once all the caulking is completed. There are many potential spots along a wall where the caulking may not be properly applied, resulting in openings in the air, moisture and vapor barrier membrane. Furthermore, the durability of the seal relies on the durability of the caulking around each anchor.
One recent attempt to solve this problem is described in U.S. Pat. No. 6,131,360 to Van Dalen. Van Dalen describes a one-piece anchor body having an inner portion for connecting to the steel back-up wall, an outer portion for connecting to the masonry and an intermediate flange between and integral with the inner and outer portions. The membrane flange extends outwardly in all directions and sits flush against the exterior sheathing of the back-up wall so that a membrane applied to the exterior sheathing may be lapped and sealed all around the outer portion of the anchor body without the need for any additional caulking or other applications. One of the problems with the one-piece anchor described by Van Dalen, however, is that it must be inserted through the exterior sheathing from the outside, and requires coordinated and simultaneous labour on the inside of the wall to attach the anchor to the stud. One other problem with the one-piece anchor is that, while it improves the quality and durability of the seal around each anchor, it does not provide for efficient and simple installation of membrane over a smooth uninterrupted surface. While this may not create a significant air leakage problem due to the presence of the membrane flange, it still creates an extra step during installation as care must be taken to properly position the membrane prior to piercing by the anchor body. Yet another problem with all current, one-piece anchors is that the conductive anchors act as thermal bridges through the insulation layer, whereby heat flow through the anchors reduces the effectiveness of the thermal protection provided by the wall assembly.